(1) Field of the Invention
The present invention relates to a method and apparatus for transmitting pressure utilizing a pressure transmitting medium.
(2) Description of the Related Art
A gas (e.g., air) or a liquid (e.g., oil, water) is conventionally used as a pressure transmitting medium in a pneumatic apparatus or a hydraulic apparatus. Such a pressure transmitting medium is also utilized by a hot isotatic pressing (HIP) apparatus, an extruder for metal, and the like used under high temperature operating conditions.
A liquid medium can generate a pressure higher than that generated by a gas medium, since a liquid has a compressibility much smaller than a gas. There are generally problems with oil, such as inclusion of gas (air), decrease of its compressibility under a very high pressure condition, and an upper limit (up to 200.degree. C.) of its service temperature. Such an upper service temperature limit is determined since oil can burn when used at a high temperature. Furthermore, the liquid and gas are apt to leak due to fluctuations in temperature and pressure, particularly under a high pressure condition, so that the sealing structure must be complicated. Still further, if part of the feeding system of the liquid or gas under pressure breaks, the liquid or gas will spout out from the broken part.